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    <title>Document</title>
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  <body>
    <script>
      var o = {
        a: 10,
        b: {
          fn: function() {
            console.log(this.a) // undefined
            console.log(this) //o.b
          }
        }
      }
      //调用
      o.b.fn()
    </script>
  </body>
</html>
